In Long-Term Evolution (LTE) by the 3rd Generation Partnership Project, the Radio Access Network is optimized for packet-oriented applications with low latency and high-peak rates. In order to guarantee that the packets are correctly delivered to the upper layers, LTE employs a combination of Automatic Repeat Request and Forward Error Correction, also known as Hybrid-ARQ, which must be fed back to a base station. In the uplink, the uplink control channel called the physical uplink control channel (PUCCH) is associated with the transmission of Channel Quality Indicators, Hybrid-ARQ acknowledgements and scheduling requests. Within the PUCCH, multiple User Equipments can share the same time-frequency resources, the User Equipments being multiplexed via Code Division Multiplexing in the frequency domain and in the time domain, simultaneously. For Channel Quality Indicators information, for instance, Code Division Multiplexing is achieved by cyclically shifting a code exhibiting Constant Amplitude Zero Autocorrelation property. This is based on the fact that cross-correlation is null among cyclically shifted Constant Amplitude Zero Autocorrelation codes.
LTE PUCCH determines a signal to noise ratio (SNR) or Signal to Interference-plus-Noise Ratio (SINR) associated with each User Equipment. LTE PUCCH SNR or SINR may then be used as a reference value during power control procedure. Accurate estimation of the SNR/SINR ensures that each User Equipment can appropriately adjust its transmitting power so as not to unduly generate interference over other User Equipments and also avoids unduly wasting battery power. LTE specifications do not specify how LTE PUCCH SNR/SINR should be determined. Conventional methods usually determine separately the noise power level and the signal power level associated with each UE, each being derived based on estimates of the channel over which the LTE PUCCH signal was transmitted. Unfortunately, such methods tend to be inaccurate where timing errors are experienced due to the fact that orthogonality between CAZAC codes is often lost in Orthogonal Frequency Division Multiplexing (OFDM) systems such as LTE. In such cases, timing errors can cause a linearly growing phase error within OFDM symbols which ultimately impair the accuracy of the LTE PUCCH SNR.
This situation is problematic, mostly where several User Equipments are piggy-backed by the PUCCH, since the combination of a plurality of timing errors has the effect of limiting the capacity of the PUCCH carrying more User Equipments at the same time.
Therefore, it would be desirable to have a solution that would determine the PUCCH SNR/SINR without suffering from the negative impact of the timing errors.